Multi-cavity injection molds require a manifold with passages leading from the manifold to the respective mold cavities. The common practice has been to have an inlet passage at the back of the mold and through which a plasticizer injects molten plastic into a manifold that extends at right angles to the inlet passage. Such manifolds have branch passages leading to the individual cavities of the mold and extending at right angles to the manifold.
The injected material has had to flow around a right angle in entering the manifold from the inlet passage, and then flow around another right angle in order to pass from the manifold into the respective cavities. In such a manifold system, the flow of the molten plastic is at very different velocities at different places in the cross-section of the manifold system. Material can accumulate along sides or at changes of direction of the main flow of the material, and such accumulated material may remain in one place for extended periods.
With heat-sensitive materials, such delays in passage through the manifold provide sufficient time for deterioration and, if the material eventually reaches the mold cavities, the products made by injection blow-molding apparatus are not uniform and some of them are defective.
This invention has the manifold open through one side of the mold instead of being supplied through an opening at the back of the mold. Thus the molten material from the plasticizer flows into the manifold in the same direction that the material in the manifold flows to the branch passages leading to the mold cavities. The preferred embodiment of this invention has the manifold taper to progressively smaller cross-section as it leads away from the inlet end, and has branch passages which extend at acute angles to the axis of the manifold so that plastic material enters the branch passages with a change of direction substantially less than 90.degree. . The manifold has no dead spaces in which plastic material can accumulate, and all of the material in the manifold flows at substantially uniform rates of flow.
The inlet end of the manifold is preferably located under the path along which the core rods travel from the injection mold to a blowing mold. This permits the manifold to be located where the branch passages can communicate with the mold cavities at the neck end of the cavities for more uniform temperature distribution in the individual cavities. The stationary portion of the mold is constructed with the manifold low enough so that the portions of the plasticizer that extend under the path of movement of the core rods is below the level of the core rods when they move from one mold to the next.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.